Manufacture of artificial silk



Patented Jan. 17, 1939 UNITED STATES MANUFACTURE OF ARTIFICIAL SILK Hayden B. Kline and Emerson B. Helm, Cleveland, Ohio, assignors to Industrial Rayon Corporation, Cleveland, Delaware Ohio, a corporation of No Drawing. Application August 23, 1934," Serial No. 741,146

1 Claim.

This invention relates to the manufacture of color-fast delustered artificial silk; more particularly, to the manufacture of artificial silk having at once a. pleasing subdued luster closely approxi-' I mating that of natural silk and a color fast not only to the effects of washing, bleaching-and like operations but also to the action of light and other natural agencies. Color-fast artificial silk manufactured pursuant to practice of the present 10 invention owes its color to the incorporation in the mass from which it is spun of the desired dyestuff, a feature that obviates the technically difflcult procedural step of subjecting the product to a dyeing operation after washing, desulphuriz- 1 ing and bleaching or otherwise treating it. Artificial silk manufactured by the process of the present invention is not lustrous in the same degree as colored delustered artificial silk dyed in thread or fabric form, but, due to the incorpora- U tion of the coloring material in the mass from which it is spun, has, quantity for quantity of I delusterant, a luster more nearly approaching that of natural silk. At the same time, it differs from and has important advantages over artificial silk heretofore colored by adding a dyestuff to the mass from which it is spun in that it is delustered by means of an oleaginous or inorganic pigment delusterant.

It is common practice to incorporate in the I mass from which artificial silk is spun a delusterant that serves to difiuse to agreater' or less extent any light striking the surface of the artificial silk other than that physically absorbed and that reflected by the phenomenon spoken of as to specular reflection. The theory advanced to eX-.

by the incorporation of delusterants in artificial l silk, which, as is generally known, is nearly optically void, is that the delusterant refracts and re- 40 fleets almost endlessly any light entering the body of the artificial silk that does not become absorbed in the course of such refraction and reflection. Lustrous artificial silk; i. e., artificial silk containing no delusterant, does not diffuse 46 any very considerable part .of the light that strikes it, but instead transmits such light without a great .deal of absorption, refraction or reflection other than specular reflection, from which property it derives the transparency that 50 it evinces in thin sheet form and the metallic luster that characterizes it in the form of thread" and fabric. By the interposition of a delusterant, it is thus possible to impart a degree of opacity to artificial silk that artificial silk alone does not ll possess, taking advantage in obtaining such deplain the high degree of diffuse reflection obtained gree of opacity of the diffuse reflection resulting from the almost endless internal reflection and refraction within the body of the artificial silk of light that is neither reflected by specular refiection at the surface nor physically absorbed, 5 immediately or ultimately.

In the case of artificial silk that is to be used in undyed condition, there is no disadvantage connected with the incorporation of a delusterant in this manner; in fact, in the case of undyed artificial silk the incorporation of a delusterant provides a wholly satisfactory method of imparting the desired degree ofopacity. When, however, artificial silk delustered in this fashion is dyed, diificulties are met with in that the efiect 16 of the delusterant is in part lost due to the markedly higher concentration of the dyestufl at or just below the surface of the artificial silk, as most readily revealed, for example, by microscopic examination of individual filaments of artificial 20 silk of relatively high denier. This follows inevitably from the dyeing of the artificial silk in thread or fabric form, for to a certain extent, depending upon the color to which the artificial silk is dyed, this markedly higher concentration 26 of dyestufi' at or just below the surface of the artificial silk cannot but result in absorption to a greater extent than otherwise of so much of the light striking the surface of the artificial silk as is not reflected by specular reflection. There 30 may or may not be a change of consequence in the amount of light reflected by specular.reflection, but of that not so reflected the proportion absorbed is naturally increased-by the presence of this markedly higher concentration of the dyestuff at or just below the surface. Obviously, as the color of the dyestuif ranges from off-white to near-black, the greater is the proportion so absorbed. This difficulty is not known to have been recognized heretofore, but, if recognized, has not heretofore been overcome except, perhaps, by the use of unnecessarily large amounts of delusterant.

Another difficulty encountered in the dyeing of delustered artificial silk arises from the fact that the delusterant is not ordinarily dispersed in the body of the thread with complete uniformity, but somewhat'irregular. in general, this is true of artificial silk manufactured on a commercial scale regardless of the precautions taken to obtain uni- 5o formity of dispersion, probably due to settling=of the delusterant in the mass from which the artificial silk is spun. Whatever the reason may be, the fact remains that where delustered. arti-l ficial silk is dyed in the usual way, the dyestufi' on is more or less irregularly adsorbed, resulting in a lack of levelness that, while perhaps not of consequence for all purposes, nevertheless constitutes at times a most serious disadvantage. In any event, it is true that the dyeing qualities of artificial silk dyed in thread or fabric form depend in part at least upon the dispersion of the delusterant, which, as pointed out above, is not ordinarily completely uniform. Thus it is unusual to obtain absolute dyeing uniformity where artificial silk containing a delusterant isdyed in the form of thread or fabric.

It is, further, old to manufacture lustrous artificial silk by the viscose process by incorporating in the viscose from which the artificial silk is spun a dyestuff capable either of going through the spinning and subsequent steps in the process of manufacture without decomposition or of assuming the desired color upon. oxidation in the spinbath or in the course of later steps entering into the process of manufacture. Thus United States Patent No. 1,865,701 discloses the manufacture of lustrous artificial silk in which the final color is produced by oxidation, there being employed to this end a dyestufi capable of being reduced by the compounds present in the viscose from which the artificial silk is spun and of being oxidized in the course of, or'subsequently to, the spinning operation. As pointed out in the specification of that patent, it has been found expedient in these circumstances to depart from the preferable procedure of reducing the dyestuff by means of such desirable reducing agentsas sodium hydrosulphite, forming instead a paste with a dilute solution of caustic soda and adding this paste, without prior reduction, to the viscose. The reason given for this departure from preferred procedure is the tendency of dyestuffs reduced by the usual reducing agents to stabilize the viscose and interfere with its proper ageing. By following the procedure described in the patent, constituting a modification of the perferable method of reducing the dyestuff and adding it in reduced condition to the viscose, it is said to be possible to manufacture lustrous artificial silk without experiencing the difi'lculties mentioned.

Among other things, it has been found that these difiiculties are not encountered in the process of artificial silk manufacture to which this invention relates, a contrary result that makes it possible to employ in the manufacture of delustered artificial silk by the viscose process the preferable dyeing procedure of reducing the dyestufi by means of sodium hydrosulphite, adding the resulting leuco compound to the viscose, and oxidizing. It is not necessary in the manufacture pursuant to this invention of color-fast delustered artificial silk to follow the procedure disclosed in the patent of forming a paste with dilute caustic soda solution and adding the paste so formed to the viscose, depending upon the uncertain action of the reducing agents present in the latter for the reduction of the dyestuif. Not only is proper ageing arrived at without departure from the usual methods, but in addition the quality of the dyeing is dependent upon the uniformity of dispersion of the delusterant to a much less extent than otherwise; likewise, there is no markedly higher concentration of dyestuff at or just below the surface of the artificial silk to increase the amount of light physically absorbed and thereby impair the opacifying effect of the delusterant'. The invention makes it possible toobtain without substantial interference from the dyestufi virtually the entire effect of the delusterant; also, to avoid dyeing irregularities arising out of non-uniform dispersion of the delusterant in the body of the artificial silk. Furthermore, color-fast delustered artificial silk of the kind to which the invention relates owes its color not to the presence. in the artificial silk of a zone of limited cross-sectional area in which is found an unusually high concentration of the dyestuff, but to the presence of the dyestuff, in lesser concentration, more or less uniformly throughout the body of the artificial silk. These various advantages, together with others which will be readily apparent to those siklled in the art, flow from the practice of the present invention,

For purposes of illustration, the invention will be described more fully in connection with the manufacture of colorfast delustered artificial silk manufactured by the viscose process, but it will be understood that in its broader aspects it is applicable not only to artificial silk manufactured by the viscose process but to other forms of artificial silk as well. Similarly, while the invention will be described for convenience in connection with the manufacture of artificial silk having more or less of a pink color, it is obviously equally practicable to produce by the practice of the invention delustered artificial silk of other colors than pink, depending on the dyestuif or dyestuffs employed, this following from the fact that any otherwise suitable dyestufi, regardless of the color which it imparts to the product, may be used in the practice of the invention. Further for purposes of illustration, the invention will be described with particular reference to the use of the so-called vat dyestuffs, although in this connection' it must be borne in mind that the invention is not limited in its usefulness to the employment of these particular dyestuffs, but, with appropriate changes in the details of the procedure followed, can be used to equal advantage with other dyestuffs, as, for example, sulphide dyes and even direct dyes capable of going through the spinning and subsequent steps in the process of artificial silk manufacture without decomposition or impairment in other respects of their dyeing properties.

Pursuant to the practice of the invention, artificial silk manufactured by the viscose process is delustered and given a fast pink color by the incorporation in the viscose prior to spining of a vat dyestuff, preferably reduced as hereinafter outlined by means of sodium hydrosulphite; an oleaginous material such as white mineral oil; and finely divided titanium dioxide, preferably in an amount ranging from .005 to .008% based on the weight of the viscose. For purposes of illustration, the dye concentration may conveniently be assumed to be in the neighborhood of .005%, based on the weight of the viscose, corresponding to a dye charge of approximately 6.8 grams of dyestuff for each 300 pound batch of viscose to be dyed. Assuming the use of a dye charge of 6.8 grams, this amount of dyestuif is weighed out and introduced into a 250 cc. Erlenmeyer flask, to which are then added 140 cc. of a 2.5% aqueous solution of caustic soda, after which the fiask is stoppered and well shaken to break up any lumps of dye'stuff. The unstoppered flask is then heated until incipient boiling occurs, after which the flask is removed from the source of heat and 2.7 to 2.8 grams of anhydrous sodium hydrosulphite are introduced. After closing the flask with a dry rubber stopper, the contents of the flask are agitated to insure contact between the reducing liquor and the dyestuff for the purpose of effecting reduction and solution of the latter, After cooling, the contents of the flask are added to the viscose, to which have previously been or are thereafter added the finely divided titanium dioxide'and any other substance or substances, such as the white mineral oil, that it may be desired to introduce. In any case in which an oleaginous material, such as the white minera oil, is incorporated in the mass, the amount thereof may vary within wide limits; but where employed, as in the example given, in conjunction with titanium dioxide, the amount thereof may conveniently be in the neighborhood of .50%, based on the weight of the viscose.

Among the vat dyestuffs that may be incorporated in this;.:way may be mentioned Sulfanthrene Red 3""B'(paste) Ponsol Pink B (double paste), Anthrene Red BN (paste), Helio Fast Pink RL (powder), Thianthrene Pink FB (double powder), Sulfanthrene Pink FB (paste), Pyanthrene Brilliant Pink FF (powder), Sulfanthrene Pink FF (paste), Algol Pink B (powder), su1f-' anthrene Scarlet 2B (paste), and Sulfanthrene Scarlet G (paste), as well as mixtures of the same, such, for example, as mixtures of Thianthrene Pink FB (double powder) and Helio Fast Pink RL (powder), The optimum concentration will, of course, depend on the particular dyestuff or dyestuffs employed, the mass from which the artificial silk is to be spun, and the color that it is desired to impart to the final product and in any given case will preferably be experimentally determined; but in general concentrations may be employed, based on the weight of the spinning mass, ranging in the case of pastel shades from approximately .001 to approximately .01%, in the case of medium shades from approximately .005 to approximately .05%, and in the case of dark shades upwards of approximately .03%.

' By way of example of concentrations of vat dyestuffs that may be employed in the production of pleasing shades of pink may be mentioned the concentrations of .012% for Sulfanthrene Pink FB (paste), .025% for Anthrene Red BN (paste), and 004% for Algol Pink B (powder) also, when used together, concentrations of .0025% and .0010%, respectively, for Thianthrene Pink FB (double powder) and Helio Fast Pink RL (powder). Obviously, the vat dyestuffs mentioned are but typical of the available commercial vat dyes, which include indigo, the various halogen derivatives of indigotine, methyl and tolyl indigotine, ciba colors, thioindigos, helindone dyes, indanthrene dyes and others.

In the preceding illustrative example, titanium dioxide and white mineral oil, employed conjointly, constitute the delusterant. It will be understood that it is by no means necessary in the practice of the invention that oleaginous and inorganic pigment delusterants be used together, for either an oleaginous delusterant or an inorganic pigment delusterant may be used to the exclusion of the other. Similarly, where an inorganic pigment delusterant is used to the exclusion of an oleaginous delusterant, it is not necessary that it consist solely of titanium dioxide; it may, if desired, be compounded of titanium dioxide and any other suitable inorganic pigment or, to the exclusion of titanium dioxide itself, of one or more other suitable inorganic pigment delusterants. As examples of inorganic pigment delusterants that may be used in lieu of or in conjunction with titanium dioxide may be mentioned barium sulphate, thorium oxide and zirconium oxide. Pine oil is an example of an oleaginous delusterant that may be used in place of or in conjunction with white mineral oil, either as such or together with an inorganic pigment delusterant.

The conjoint use in the manner described of a delusterant such as titanium dioxide, white mineral oil or both, and a dyestuff that can to advantage be incorporated in the mass from which the artificial silk is spun, either by virtue of the fact that it is capable of going through the process of artificial silk manufacture without decomposition or by virtue of the fact that it may be introduced into the mass in reduced condition and oxidized in the spinning or subsequent operations to develop its color, is without procedural complications. Based upon microscopic examination of viscose containing a delusterant comprising titanium dioxide and white mineral oil and a vat dyestuff introduced into the mass in reduced condition, there is reason for believing that the dyestufl. is in some degree adsorbed on the surface of the titanium dioxide, but the exact extent to which this. occurs it is of course difiicult or impossible to determine. It is probable that while part of the dyestuff becomes adsorbed on the surface of the titanium dioxide, part, since the dyestuff is introduced into the mass in soluble form, becomes uniformly distributed in the body of the artificial silk, being held either in a state of adsorption or a state of chemical combination. At any rate, no departure from the usual process of manufacturing artificial silk other than as involved in the actual introduction of the dyestufl is occasioned.

Thus the invention eliminates disadvantages arising out of the dyeing in thread or fabric form of delustered artificial silk. Among other things, lack of uniformity of the dispersion of the delusterant affects the evenness of the dyeing to a less extent than otherwise would be the case, for the dyestuff is not, as heretofore, introduced after, but rather before, the spinning of the artificial silk. Similarly, the impairment of the delustering effect of the delusterant occasioned by, the markedly higher concentration of dyestuflf at or just below the surface of artificial silk dyed in the usual way in thread or fabric form is obviated, this as a result of the incorporationof the dyestuff. It is unnecessary in the practice of the invention to depart from the practice of reducing the dyestuif by means of a reducing agent such as sodium hydrosulphite, a procedure preferred among dyers for the reason, among others, that it is possible to obtain with such reducing agents as sodium hydrosulphite a completely and uniformly reduced dyestufl. In general, the invention provides a simple method of manufacturing delustered colored artificial silk that is fast to washing, bleaching and like operations without modifying too greatly the procedure in use in the spinning of undyed delustered artificial silk,

which latter constitutes at the present time the color-fast are intended to express the thought of relative fastness to the agencies, chemical and otherwise, to which artificial silk is ordinarily subjected, but are not intended to imply fastness to unusual chemical treatments, as, for example, by reducing agents, that temporarily impair the color of vat and other dyestufis by actual chemical reduction of the same. It is intended that the patent shall cover, by suitable expression in the appended claim, whatever features of patentable novelty reside in the invention.

We claim: I

In the manufacture by the viscose process of color-fast delustered regenerated cellulose thread, the steps of reducing a vat dyestuif to a leuco base capable, upon regeneration of the cellulose content of 'the viscose, of incidental oxidation serving to develop the color which it is desired to impart to the thread; disseminating the dyestuff in the form of its leuco base throughout the viscose of which the cellulose content is to be regenerated in the course of the operation of forming the thread; disseminating throughout the viscose a finely divided delusterant comprising at least in part titanium dioxide in order that substantial opacification of the thread to be formed from the viscose may be effected; and thereafter extruding the viscose through a spinneret into a regenerating bath to regenerate the cellulose content thereof and, incidentally to such regeneration,-to oxidize said leuco base, whereby without substantial impairment of the opacitying efiect of the delusterant the thread is caused to assume a color fast not only to the effects of washing, bleaching and like operations but also to light and other natural agencies.

HAYDEN B. KLINE.

EMERSON B. HELM. 

